As the demand for improved semiconductor devices increases the need for improved semiconductor wafer lithography stage control will also continue to increase. Conventional approaches to controlling wafer stage actuation include the use of end bumpers for crash protection in event of stage runaway. Actuation of a given wafer stage (e.g., XY wafer stage, or stacked X-stage and Y-stage) is typically carried out using a servo system having stage motors suitable for “turning around” the given stage on its scanning path underneath a given radiation source (e.g., e-beam column). Typically, turnaround systems are configured to turn around the actuating stage before making contact with the bumper at either end of the scanning path. In conventional systems, under normal operational settings (i.e., no run away malfunctions), the bumpers located at each end of the scanning path have no active role. In conventional settings, it is only during run away malfunction that the bumpers of a wafer stage system take on an active role.
As wafer stage accelerations continue to increase, and turnaround frequency increases, generated wafer motor heat has little time to dissipate through the stage and to the external surroundings, an effect compounded in vacuum stage applications. The inability to dissipate heat is particularly problematic in metrology settings due to the associated thermal drift. The generated heat typically can only be dissipated through conduction into the wafer stage and radiation from the coil to the stator, and then on to the outer stage. These transfer mechanisms are inadequate for high speed and high duty cycle stages. Further, in order to avoid burning the motors of the wafer stage, air or liquid cooling must be provided. These associate cooling hoses cause additional disturbance to fast moving stages. Therefore, it is desirable to provide a wafer stage actuation control system, which cures the deficiencies of the prior at.